Smooth muscle differs from both cardiac and skeletal muscle in that
$a$ it can act as a pacemaker for rhythmic contractions.
b. contractions of smooth muscle are not due to interactions between neighboring microfilaments.
c. neighboring cells are electrically connected by gap junctions.
$d$ neighboring cells are tightly coupled by intercalated discs.
$e$ the membranes of smooth muscie cells are depolarized by stretching.